Environmental Earth Sciences

, Volume 67, Issue 3, pp 889–910 | Cite as

Integrated geophysics and soil gas profiles as a tool to characterize active faults: the Amer fault example (Pyrenees, NE Spain)

  • M. ZarrocaEmail author
  • R. Linares
  • J. Bach
  • C. Roqué
  • V. Moreno
  • Ll. Font
  • C. Baixeras
Original Article


The combined use of geophysical and soil gas composition exploration methods allows to rapidly obtain at relative low cost information that might be related to seismic activity conditions. In this study, we carried out geochemical soil gas sampling (222Rn, 220Rn and CO2), electrical resistivity tomography and seismic refraction profiles in two selected zones near the town of Amer in the Spanish Pyrenees, where the presence of recent fractures is evident in the field. Data analysis clearly reveals anomalous values for each gas at specific positions along the electrical imaging transects. Geomorphologic and hydrogeologic data and the integration of geophysical data and soil gas measurements indicate that: (1) endogene gases radon (222Rn) and carbon dioxide (CO2) are released from the meta-sedimentary basement rocks across the main fractured zones with higher permeability values, while lower Cenozoic detrital sedimentary formations act as an impervious boundary; (2) sites with highest radon concentrations (52 kBq m−3) coincide with the zones in the Amer fault showing more recent geomorphic evidence of activity, and more specifically with those areas covered by thinner surficial formations; (3) the lowest 222Rn values (0.2–0.4 kBq m−3) were recorded just on the master active fault plane. This pattern could be explained by a dilution effect resulting from high rates of soil CO2 efflux (267 g m−2 day−1); (4) soil thoron (220Rn) activity is maximum (143 kBq m−3) in areas with high surficial fracturing; (5) groundwater pumping may cause important distortions in the natural flow dynamics and in the measured concentrations of gases. The agreement between the different data (geochemical, geophysical, and hydrogeological) and field observations (geology and geomorphology) leads us to propose a preliminary tectonic-gravitational model for the study area.


Active fault Electrical resistivity tomography (ERT) Seismic refraction Soil radon and thoron activity concentration Soil CO2 efflux Pyrenees Spain 



We would like to thank three anonymous reviewers for their very constructive comments and suggestions on the earlier version of this manuscript. The study has been partially financed by the Spanish Consejo de Seguridad Nacional project CSN2009-0001-C02-01and Education and Science Ministry (project CGL2005-02404). David Soler translated a first version of the manuscript.


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • M. Zarroca
    • 1
    Email author
  • R. Linares
    • 1
  • J. Bach
    • 1
  • C. Roqué
    • 2
  • V. Moreno
    • 3
  • Ll. Font
    • 3
  • C. Baixeras
    • 3
  1. 1.Grupo de Geodinámica Externa e Hidrogeología, Dpto. de Geología, Edificio CcUniversitat Autònoma de BarcelonaBellaterra, BarcelonaSpain
  2. 2.Geodinámica Externa, Dpto. Ciencias AmbientalesUniversitat de GironaGironaSpain
  3. 3.Grupo de Física de las Radiaciones, Dpto. de Física. Edificio CcUniversitat Autònoma de BarcelonaBellaterra, BarcelonaSpain

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